Process for the manufacture of anthranilic acid



@atented ay 6, i924.

caress BRADNER, or nnenwoon,

EROCESS FOR THE MANUFACTURE ANTHRANILIC ACID.

No Drawing.

To all whom it may concern.

Be it known that we, (1) FRANK H. BEALL and (2) DONALD B. BRADNER, citizens of the United States, residing at (1) Baltimore,

(2) Edgewood, in the counties of (1) Baltimore, (2) .Harford, and State of Maryland, have inventedcertain new and useful Improvements in Processes for the Manufacture of Anthranilic Acid, of which the following is a specification.

This invention relates to the manufacture of amino-benzoic acids by reduction of the nitro-benzoic acids and more particularly to the manufacture of anthranilic acid (o-amino-benzoic acid) by the reductionof o-nitro-benzoic acid.

A process for the manufacture of anthranilic acid described in the literature consists in reducing o-nitro-benzoic acid by means of tin and hydrochloric acid, precipitating the tin with hydrogen sulfid, evaporating the solution, treating the concentrate with ammonia to alkaline reaction and then acidifying with acetic acid and recovering the anthranilic acid from the reaction mixture by crystallization. This process is impractical for commercial use particularly on account of the disadvantage of havingthe tin used in the process left in the form of the sulfid.

In an application filed by Frank H. Beall on July 8, 1922, Serial No. 573,715, is described an improvement upon said process described in the literature which comp-rises the reduction ,of the nitro group of nitrobenzoic acids to the amino group by the action of metals having a reduction potential greater than tin; this reduction requiring careful control of the reducing conditions.

We have discovered a method of making amino-benzoic acids by reduction of nitro benzoic acids by means of metals having a reduction potential less than that of iron which is superior to the above-mentioned process of reducing with tin and hydrochloric acid, and which is also free from the necessity for the-careful control of re ducing conditions of the process described in said application;

The preferred metal for this process is copper and the invention will be described hereinafter by reference to the use of copper and the manufacture of anthranilic acid (o-amino-benzoic acid) from o-nitro-benzoic acid, it being understood however that the invention is not limited to the manufacture Application filed July 8, 1922. Serial No. 573,689.

of anthranilic acid or to the use of copper but includes the manufacture of other amino-benzoic acids, the meta and para acids, and the use of other metals, such as tin, havmg the characteristics referred to, that is, a reduction potential less than that of iron, but lnsuflicient to reduce the nitro group of nitro-benzoic acids to the amino group. Other metals which may be used may be selected by reference to the known electrolytic potential and solubility tables.

The process is illustrated in the following specific examples it being understood howeverthat the invention is not limited to the particular reagents, proportions and procedure described except as is required by the appended claims.

Ewample 1.10 parts by weight of c-nitro-benzoic acid are mixed into a solution of 15 or 16 parts by weight of 100 per cent sulfuric acid in 50 to 100 parts by weight of water and finely divided copper, preferably precipitated copper, is added in excess of the theoretical quantity. The mixture preferably is heated to about 100 C. and stirred until the reduction is complete which usually occurs in from 1 to 2 hours at the temperature mentioned. Under these conditions about to per cent of the anthranilic acid product is precipitated in the form of the co per salt during the reduction. The precipitation of the copper salt is completed by the addition of alkali or other neutralizing agent in quantity sufficient to substantially neutralize the acidity of the solution. The precipitated copper salt of anthranilic acid with undissolved copper is separated. from the copper sulfate solution and washed and is then digested with alkali, such as caustic soda, preferably at an elevated temperature whereby the cop per salt of anthranilic acid is decomposed forming a precipitate of copper oxid or hydroxid and a solution of the sodium salt of anthranilic acid. The solution of the sodium salt is separated from the solid residue of copper and copper oxid or hydroxid and the anthranilic acid recovered from the solution by acidifying in the known manner.

The residue of copper and copper oxid or hydroxid may be returned directly to the process in a succeeding batch.

The copper in the copper sulfate solution may be recovered in the form of precipitat ed copper for reusein the process by prebenzoic acid is mixed with a solution of 24 to 28 parts by weight of sulfuric acid of 66 B6. in 100 parts by weight of water. An excess of precipitated copper is added and the mixture stirred and heated to 100 C. for from one. to twohours. At the end of the reduction the reaction mixture is diluted with about 100 parts by Weight of water and scrap iron is added in quantity sutlicient to precipitate the dissolved copper. The solution which now contains the anthranilic acid and ferrous sulfate is separated from the metallic copper and the acidity of the separated solution is reduced to the point at which substantially all of the anthranilic acid is precipitated in the form of the iron salt. Any suitable neutralizing agent may be employed such as sodium hydroxid, ferrous hydroxid or sodium sulfite. The iron salt of ant'hranilic acid is separated and converted to the soluble sodium salt by digestion with sodium hydroxid, the iron content of the iron salt being converted to ferrous hydroxid. The solution of the sodium salt of anthranilic acid is separated from the terrous hydroxid and neutralized in the known manner to recover anthranilic acid.

It will be seen from example 1 that the quantity of mineral acid used in the reducing operation may be as small as about 5 hydrogen equivalents for each molecule of nitrobenzoic acid to be reduced, that. is, a quantity substantially less than that theoreti -ally required to supply sufticient hydrogen for the reduction. It will further be seen from examples :2 and 3 that a greater amount of acid may be employed. i

This process is simple in operation and results in an extremely good yield of anthranilic acid, 95 per cent or better. the product being substantially pure.

A. distinct advantage of the process resides in the fact that the metal employed in the reduction is economically recovered in form for reuse in the process, consequently the more expensive metals having the most desirable reduction potential may be employed without introducing a prohibitive element of expense into the process.

he expression reduction potential as used in the foregoing description and in the appended claims is practically synonomous with the expression electrolytic potential" and the description of metals as having a reduction potential less than iron means that such metals are less elcctro-positive than or elcctro-negative to iron.

lVe claim:

1. Process of making amino-benzoic acids which comprises, reducing a nitro-benzoic acid to the corresponding amino-benzoic acid by the reducing action of a mineral acid and a metal having a reduction potential less than iron and capable of forming an insoluble salt with said amino-benzoic acid, and separating a metal salt of the said amino-benzoic acid from the reaction mixture.

2. Process of making amino-benzoic acids as defined in claim 1 in which copper is the metal employed.

3. Process of making amino-benzoic acids which comprises, subjecting a nitro-benzoic acid to the reducing action of a mineral acid and a metal having a reduction potential less than iron, and precipitating an insoluble metal salt of the resulting amino-benzoic acid from the reaction solution.

4. Process of making amino-benzoic acids which comprises, subjecting a nitro-benzoic acid to the reducing action of a mineral acid and a metal having a. reduction potential less than iron and capable of forming an insoluble salt with the resulting aminobenzoic acid, and reducing the acidity of the solution whereby saidinsoluble salt of the said amino-beuzoic acid is precipitated.

5. Process of making amino-benzoic acids which comprises, subjecting a nitro-bcnzoic acid to the reducing action of a metal having a reduction potential less than iron in the presence of mineral acid in quantity less than the quantity theoretically required to supply the hydrogen for the reduction.

6. Process of making anthranilic acid which comprises, subjecting o-nitro-benzo1c acid to the reducing action of copper in the presence of mineral acid in quantity less than the quantity theoretically required to supply the hydrogen for the reduction.

7. Process as defined in claim 8 in wlncn anthranilic acid is made by the reduction of o-nitro-benzoic acid.

8. Process of making amino-benzoic acids which comprises, reducing a nitro-benzoic acid to the corresponding amino-benzoic acid b the reducing action of a mineral acid and a metal having a reduction potential less than iron. precipitating an insoluble metal salt of said amino-benzoic acid from the reaction solution. digesting-the precipitated salt with alkali, and separating the resulting alkali salt of said amino-benzoic acid from the resulting metal compound.

9. Process of making amino-benzoic acids which comprises, reducing a nitro-benzoic acid to the corresponding amino-benzoic acid by the reducing action of a mineral 7 acid and a metal having a reducing potenwith iron whereby copper is precipitated, reducing the acidity of the solution whereby the iron salt of the said amino-benzoic acid is precipitated, digesting the precipitate with alkali, and separating the resulting solution of the alkali salt of said amino-benzoic acid from precipitated iron compound.

In testimony whereof, weafiix our signa- 20 tures.

FRANK H. BEALL. DONALD B. BRADNER. 

